A complete discipline of selection, temperature management, water preparation, knife work, and composed presentation. Quality is determined before the knife touches fish: in sourcing, handling, preparation of every accompanying element, and understanding that rawness demands perfection because there is nothing to hide behind.
Fish selection: sashimi-grade means parasite-treated through freezing, not 'better quality.' Mixed plate selects for contrast in texture, fat, and colour. Temperature: fish stored 0–2°C, removed moments before cutting, plate chilled 15 minutes. Water preparation of garnish is NON-NEGOTIABLE: tsuma (shredded daikon) plunged into ice water 10–15 minutes — washes out peppery bite, causes fibres to curl and become crisp and alive. Ken, shiso, all soaked and revived. Species-specific cuts: hira-zukuri (standard, 7–10mm), sogi-zukuri (angled for firm fish), usu-zukuri (paper-thin translucent), kaku-zukuri (cubes). Plating: odd numbers, asymmetric, lean fish left to rich fish right (eating progression), tsuma as structural base, space is intentional.
Quality hierarchy: 1) fish freshness, 2) knife sharpness, 3) water preparation of garnish, 4) temperature control, 5) knife technique, 6) plating. If your daikon tsuma doesn't curl and spring when lifted from ice water, it's cut too thick or hasn't soaked long enough. Real wasabi loses volatile compounds within 15 minutes — grate at the table. Soy should be shallow enough to dip not drown.
Not soaking tsuma and garnish in ice water — produces harsh, limp, dead-tasting garnish. Cutting all fish same thickness. Multiple knife strokes per slice. Plating fish flat on bare plate. Mixing wasabi into soy sauce. Serving on warm plate. Cutting too far in advance. Dull knife. Not wiping blade between cuts.